Prosthetic element, particularly a tooth post made of composite material

ABSTRACT

PCT No. PCT/FR95/01532 Sec. 371 Date Dec. 15, 1997 Sec. 102(e) Date Dec. 15, 1997 PCT Filed Nov. 21, 1995 PCT Pub. No. WO96/15759 PCT Pub. Date May 30, 1996A shaped member made of composite material for making a prosthetic element, particularly a tooth post, comprising a core of longitudinal fibers embedded in a resin matrix, and a method for making the member, are disclosed. The member is characterized in that the resin matrix contains at least one metal oxide.

FIELD OF THE INVENTION

The present invention relates to a section of composite materialintended to constitute a prosthetic element, and particularly a toothpost, as well as to a process for manufacturing such a section.

BACKGROUND OF THE INVENTION

It is known that, in the dental domain, in order to ensure the perennityof the dental substance of a tooth, metal posts are called upon, whichare screwed or sealed therein. Such metal posts present a certain numberof drawbacks, which are principally associated with the great differencewhich exists between the mechanical characteristics of these posts andthose of the dentine in which they are disposed.

In order to avoid such drawbacks, it has been proposed to employ postsmade of composite material, constituted in particular by a matrix ofbio-compatible resin, and particularly an epoxy resin, in which carbonor glass fibers are embedded.

In certain embodiments, the fibers are longitudinal fibers which extendover the whole length of the post and which are under equal tensiontherein. The posts thus constituted, by reason of their mechanicalcharacteristics close to those of the dentine, considerably reduce thedrawbacks set forth hereinabove.

However, such posts present the drawback of being transparent to X-rays,so that their positioning is particularly difficult to establish withthe aid of the conventional apparatus available to practitioners.

These posts are usually manufactured by pultrusion, i.e. by a process ofextrusion in which both the fibers, particularly the carbon or glassfibers, and a resin matrix are passed in the same die at the same time,the fibers being, all along the operation, maintained under tension.This operation of pultrusion is sometimes difficult to carry out byreason of the problems of obturation of the die of the extruder whichoccur during operation.

In the prior state of the art, products, or charges, are known, whichare added to the dental reconstitution pastes, in order to give them acertain opacity to X-rays. U.S. Pat. No. 4,503,169 thus proposes to thatend to include zirconium, oxides in dental reconstitution pastes.

Patent GB-A-2 028 855 also discloses a settable composition exempt ofmercury based on a carboxylic polyacid and which contains, inter alia,filling elements which may possibly comprise fibrous elements which maybe coated with metal oxides capable of reacting with the carboxylicpolyacid in order to promote bond with the matrix.

SUMMARY OF THE INVENTION

The present invention has for its object to propose a means for solvingboth the problems associated with carrying out the pultrusion operationand those connected with the lack of opacity of the prosthetic elementsused in the dental art, which are constituted by composite materialsbased on resins, particularly epoxy resins, reinforced by fibers,particularly long, unidirectional carbon fibers.

The present invention thus has for an object a section of compositematerial intended to constitute a prosthetic element, particularly adental post, comprising a core, constituted by longitudinal fibers,which is embedded in a matrix of resin, characterized in that this resinmatrix contains at least one metal oxide.

Applicants have in fact observed that the implementation of pultrusionwas largely facilitated when metal oxides were added to the resinmatrix. In fact, the added metal oxide behaves like a sliding agentwhich reduces the adhesion of the resin and promotes flow of the productin the die of the extruder. Implementation is even easier when the metaloxides are in the form of granules or microballs. It is also possible,in order to facilitate the pultrusion operation further, to use metaloxides which are contained in microballs, particularly glass microballs.

Under these conditions, the metal oxides introduced in the resin performtwo functions, namely a first function of slide provoking the extrusionand a second function of opacity.

As set forth hereinafter, when one is obliged to add a relatively largequantity of metal oxides in the resin, oxides contained in glassmicroballs are totally or partly employed. A plurality of particles ofoxides may, moreover, be grouped in the same microball.

According to the invention, the metal oxide or oxides chosen, necessaryfor giving the desired opacity to the prosthetic element, may beassociated, wholly or partly, with the fibers, i.e. it is eitherintroduced therein or disposed on their surface so as to constitute acoating adhering well thereto. In this last embodiment, the cohesion ofthe fibers with the resin is thus improved.

In an embodiment of the invention, the metal oxide presents a refractionindex higher than the refraction index of the dentine. Such anembodiment of the invention is particularly interesting in that, withidentical resultant overall opacity, the quantity of said metal oxidecontained in the resin can be reduced, which avoids diminishing themechanical qualities of the post. In addition, it is thus possible, fora given desired refraction index, to control the quantity of metal oxideused, in order to place in the post only the quantity which allows thesliding agent to act in optimum manner, which promotes the pultrusionoperation.

The present invention also has for an object a process for manufacturinga section of composite material, intended to constitute a prostheticelement, and particularly a dental post, comprising a core constitutedby longitudinal fibers, this core being embedded in a matrix of resin,characterized in that it comprises the steps consisting in mixing withsaid resin matrix at least one metal oxide, and in extruding the fibersand the resin matrix containing said metal oxide, while maintaining saidfibers under equal tension.

In an embodiment of the invention, the metal oxides may be associatedwith the fibers, i.e. be introduced in the mass thereof or on theirsurface.

At least one of the metal oxides associated with the fibers may beidentical to that, or to one of them, mixed with the resin matrix.Furthermore, the refraction index of the oxide used may advantageouslybe greater than the refraction index of the dentine.

In a particularly interesting embodiment of the invention, the fiberscoated with metal oxides receive a specific bridging agent intended topromote bonding thereof with the resin matrix, this bridging agent beingconstituted, in the majority of cases, by silanes.

The coating of metal oxide may be made on the whole surface of thefibers, particularly by a thermic impregnation, when the meltingtemperature of the fibers is higher than that of the metal oxides. Undersuch conditions, the granulometry of the metal oxides has only littleinfluence on the radio-opacity. The coating may also be made,particularly in the case of the melting temperature of the fibers beinglower than that of the metal oxide, by employing a process ofprojection, and in particular a plasma projection process.

According to this embodiment, the fibers coming from storage reelstraverse an impregnation tank where they are impregnated with metaloxide in the molten state, then these fibers are drained and dried in asecond enclosure of which the temperature progressively decreases.

BRIEF DESCRIPTION OF THE DRAWINGS

A form of embodiment of the present invention will be describedhereinafter by way of non-limiting example, with reference to theaccompanying drawing, in which:

FIG. 1 is a schematic view illustrating a general embodiment of sectionsaccording to the invention.

FIG. 2 is a schematic view of a variant embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, dental posts are constituted byincorporating in a matrix constituted by a thermosettable resin, or athermoplastic resin, metal oxides which are biocompatible, in order notto provoke problems of acceptation by the patient's organism. Thequantity of metal oxide introduced in the resin is a function of therefraction index which it is desired to obtain. These oxides preferablypresent a refraction index higher than that of the dentine, and eventhan that of the osseous structure, and preferably much greater thanthem.

It is known that the refraction index of the osseous structure is of theorder of 1.65 and that that of the dentine is of the order of 1.6. Underthese conditions, for the dental prosthetic element to be detectable byX-rays, it must present a refraction index different from that of thedentine and/or the osseous structure, viz. it is slightly higher orlower than them. The refraction indices of the dental post must thus beeither higher than 1.65 or lower than 1.6 if it is desired to be able todistinguish them both from the dentine or from the osseous structure.

The most interesting metal oxides which may thus be capable of beingused in the implementation of the present invention are:

    ______________________________________                                         magnesium oxide MgO    n = 1.74                                              strontium oxide SrO     n = 1.81                                              calcium oxide CaO.sub.2                                                                               n = 1.89                                              bariumoxide BaO             n = 1.98                                          BaO.sub.2                    n = 1.98                                         zinc oxide ZnO                n = 2.01 to 2.03                                zirconium oxide ZrO.sub.2                                                                            n =  2.13 to 2.20                                      titanium oxide TiO.sub.2                                                                              n = 2.61 to 2.90                                      ______________________________________                                    

The quantity of metal oxide introduced in the resin depends on therefraction index which it is desired to give the post.

In a first step of the process according to the invention, the metaloxide chosen is firstly blended with a resin matrix, for example bymixing. In a second step, as shown in FIG. 1, a bundle of fibers 3,particularly carbon or glass fibers, which are stored on reels 5, arepassed in a tank 1 containing the mixture of resin and chosen metaloxides. The assembly traverses a die 7 of an extruder 8 and,simultaneously to this extrusion, the fibers 3 are subjected to atension by a system of drawing constituted in known manner by"caterpillars" 9, 9'. On leaving the die 7, the composite sectionobtained is polymerized. If such a section is intended to constitutedental posts, it is then cut to the desired length and possiblymachined.

In a first example of embodiment of the invention, a mixture of epoxyresin with 25% by weight of barium oxide and 25% by weight of titaniumoxide is made. Physically, the metal oxides introduced in the resinmatrix are in the form of granules whose mean granulometry is less thanthe mean diameter of the fibers. The fibers used are high performancecarbon fibers with a diameter of the order of 8 μm, which are preferablygrouped together in tufts of 3000 to 6000 filaments. The diameter of thedie 7 is such that a section with a diameter of about 2 mm is obtainedon leaving the extruder 8. Such a section is particularly adapted to beused for making dental posts.

The radio-opacity of the section obtained has proved greater than thatof the dentine, its refraction index being 1.69. If such a section isused as dental post, it is perfectly locatable in X-ray examinationswhen the tooth is observed towards the root.

In a second example of embodiment of the invention, a mixture of epoxyresin with 39% by weight of titanium oxide is made. Physically, thetitanium fixed with the resin is, as before, in the form of microballswhose mean granulometry is of the order of 2 μm. The fibers used arehigh performance carbon fibers with a diameter of the order of 8 μm. Thediameter of the die used is the same as previously.

Upon examination, the radio-opacity of the section obtained has provedto be much greater, not only than that of the dentine, but also thanthat of the osseous structure, and that of the enamel of the tooth(n=1.65), its refraction index being 1.82, so that such a section islocatable by X-rays even through the enamel of a tooth.

As mentioned hereinabove, it was observed, during the differentimplementations of the invention, that the passage of the product (i.e.of the assembly constituted on the one hand, by the mixture of resin andmetal oxides and, on the other hand, the fibers) in the die of theextruder was rendered more difficult when the sections were of smalldiameter and necessitated large quantities of metal oxides in order toattain the desired refraction index.

In order to avoid this drawback, the fibers themselves are coated with agiven metal oxide or with a mixture of several metal oxides. In such anembodiment, the fibers may possibly receive a prior treatment intendedto promote catching thereof with the metal oxides with which it isdesired to coat them. After such a coating, the fibers may be stored ina reel while awaiting their subsequent use. Such a modus operandi makesit possible, for a determined quantity of metal oxides necessary forensuring the desired opacity, to reduce that mixed with the resinmatrix, which diminishes the compactness of the resin/metal oxidemixture and at the same time improves the passage of the product in thedie.

It is thus possible to obtain sections of composite materialincorporating carbon fibers under equal tension which present highrefraction indices, much higher than those of the adjacent osseousstructure, which presents considerable interest in numerous medicalapplications such as for example articular implants, etc.

In order to coat the fibers with the metal oxides, they are preferablypassed in a bath containing the molten metal oxides. When the meltingtemperature of a given oxide is higher than that of the fiber, which isparticularly the case when it is desired to coat glass fibers withtitanium oxide, a process of plasma projection of the metal oxide may beemployed.

In a third example of embodiment of the invention, the proportions oftitanium oxide and of barium oxide given in the first example are taken,but the barium oxide is deposited on the fibers and the titanium oxideis mixed with the resin. In this way, the fibers may be coated by hotimmersion as the high value of the melting temperature of the titaniumoxide is no hindrance, since the latter is mixed with the resin. It isthus possible, in this case, to use not only carbon fibers but alsoglass fibers since the melting temperature of the barium oxide is lessthan that of the glass.

According to the invention, the same metal oxide as that deposited onthe fibers may be mixed with the resin matrix.

More than two metal oxides may of course be mixed with the resin. Afourth example of embodiment of the invention will be describedhereinafter in which 8.5% by weight of zirconium oxide, 10.5% by weightof titanium oxide and 17.5% by weight of barium oxide are mixed with anepoxy resin.

The titanium and barium metal oxides are, in the present embodiment ofthe invention, introduced in the form of microballs. These oxides areboth included in the same glass microball with a granulometry of theorder of 20 to 40 μm. Zirconium oxide is in the form of granulates whosegranulometry is of the order of a micrometer. The fibers used are highperformance carbon fibers with a diameter of the order of 8 μm. Thediameter of the die is such that a section with a diameter of 2 mm isobtained at the outlet of the extruder.

Upon examination, the radio-opacity of the section obtained proved to beslightly greater than that of the dentine, since its refraction index is1.66. A simple dental radiograph of a section inserted in a toothconfirmed a radio-opacity of this section slightly greater than that ofthe dentine.

The metal oxides disposed in microballs proved to be particularlyefficient sliding agents, which makes it possible to introduce them inlarge quantities in the resin without provoking packing at the level ofthe die of the extruder. For a given desired refraction index, their usemakes it possible to control the quantity of metal oxide used, in orderto place in the post only the quantity which allows the sliding agent toact in optimum manner, which promotes the pultrusion operation.

In order to improve adherence of the fibers, or the fibers coated withoxides, with the resin matrix, they may be sized prior to beingintroduced in the resin. Such sizing consists, in known manner, inmaking a surface treatment of the fibers, coated or not, with the aid ofa "binding" agent whose role is to constitute a chemical bridging withthe molecules of the resin matrix.

To that end, as shown in FIG. 2, fibers 3 stored on reels 5 are admittedin an enclosure 13 heated by resistors 15, where the metal oxides 17 aremaintained in the molten state, then in a draining and drying enclosure19 where the temperature decreases progressively. At the outlet of theenclosure 19, spray means 21 project onto the fibers the binding elementchosen, and finally the treated fibers are wound on a storage reel 23.

The metal oxides may also be incorporated in the fiber itself Forexample, particularly in the case of glass fibers, the metal oxides maybe introduced in the fibers during manufacture thereof.

The metal oxides may, in the same section, be both in the form ofgranules or microballs, and in a heterogeneous form. The majority willpreferably be in the form of microballs.

What is claimed is:
 1. A shaped member made of composite materialintended to constitute a prosthetic element, comprising a coreconstituted by longitudinal fibers, said core being embedded in a matrixof resin which contains at least one metal oxide in an amount effectiveto provoke a sliding effect during extrusion, said metal oxide being inthe form of granules or microballs having dimensions which are smallerthan the mean diameter of the fibers.
 2. The shaped member according toclaim 1, wherein the metal oxide is associated with the fibers.
 3. Theshaped member according to claim 2, wherein the metal oxide associatedwith the fibers is disposed on the surface of the fibers.
 4. The shapedmember according to claim 2, wherein the fibers are glass fibers, andthe metal oxide associated with the fibers is incorporated within thefibers.
 5. The shaped member according to claim 2, wherein the metaloxide associated with the fibers is common with that or one of thosecontained in the resin matrix.
 6. The shaped member according to claim1, wherein the metal oxide presents a refraction index higher than therefraction index of dentine.
 7. The shaped member according to claim 1,wherein the metal oxide is contained in a glass microball.
 8. The shapedmember according to claim 1, wherein the fibers are coated with abridging agent intended to connect said fibers to the resin matrix. 9.The shaped member according to claim 1, wherein the metal oxide isselected form the group consisting of MgO, SrO, CaO₂, BaO, BaO₂, ZnO,ZrO₂, TiO₂, and mixtures thereof.
 10. Process for manufacturing a shapedmember of composite material intended to constitute a prosthetic elementand having a core constituted by longitudinal fibers, said core beingembedded in a matrix of resin, the process comprising:mixing aneffective amount of at least one metal oxide with said resin matrix toprovoke a sliding effect during extrusion, said metal oxide being in theform of granules or microballs having dimensions which are smaller thanthe mean diameter of the fibers; and extruding the fibers and the resinmatrix containing said metal oxide.
 11. Process according to claim 10,further comprising associating with the fibers at least one metal oxidehaving a refraction index which is higher than the refraction index ofdentine.
 12. Process according to claim 11, wherein the metal oxideassociated with the fibers is coated on the surface of the fibers. 13.Process according to claim 12, wherein the metal oxide is coated overthe whole surface of the fibers by passing the fibers in a bathcontaining at least one molten metal oxide.
 14. Process according toclaim 12, wherein the metal oxide coating is made by a process of plasmaprojection.
 15. Process according to claim 11, wherein the fibers areassociated with the metal oxide by passing the fibers through animpregnation tank containing at least one metal oxide in the moltenstate, then draining the fibers, and drying them in an enclosure whosetemperature decreases progressively.
 16. Process according to claim 11,wherein after having been associated with the metal oxide, the fibersare coated with a specific bridging agent intended to connect them tothe resin matrix.
 17. Process according to claim 16, wherein thebridging agent is a silane.
 18. Process according to claim 10, whereinthe fibers are glass fibers and the metal oxide associated with thefibers is incorporated within the fibers during manufacture thereof. 19.Process according to claim 10, wherein at least one of the metal oxidesassociated with the fibers is identical to that, or one of those, mixedwith the resin matrix.